There are several devices to reach high voltages. In one of these devices, called Marx generator, a bank of capacitors is charged up in parallel and over spark gap switches discharged in series. If the initial voltage up to which the capacitors are charged is V and if there are n capacitors charged in parallel, then the final voltage, after the capacitors are switched in series, is nV. To transmit the thusly created high voltage pulse to some load, the concept of magnetic selfinsulation first proposed by the inventor, has been proved very useful. If applied to a coaxial vacuum transmission line one utilizes the fact that the large electric current produced by the pulse and moving down the line generates a strong magnetic field acting in a direction perpendicular to the large radial electric field going down the line with the pulse. Due to this strong self-magnetic field electrons are deflected by the vxH Lorentz-force and hence are unable to cross the gap. These two concepts, the first one which is the Marx generator and the second one which is the coaxial magnetically selfinsulated transmission line, are in the invention combined in a novel way. The Marx generator concept is used to produce very large voltages and the magnetic selfinsulation concept to sustain these large voltages within the Marx generator itself. This combination permits the attainment of much higher voltages and currents.